Influence of H(2) stripping on methane production in conventional digesters

Hydrogen is a central metabolite in the methanization process. In this study the partial pressure of hydrogen in the gas phase of laboratory manure digesters was monitored over extensive periods of time and found to vary between 50 and 100.10(-6) atm. By sparging the gas phase of the digester through an auxiliary reactor, hydrogenotrophic methanogens were allowed to develop at the expense of hydrogen and carbon dioxide present in the biogas, independently of the liquid or cell residence time in the main reactor. By scrubbing ca. 100 volumes of biogas per liter reactor per day through an auxiliary reactor, hydrogen concentration could be decreased maximally 25%. This resulted in an increase in the gas production rate of the main digester of ca. 10% and a concomitant improved removal of volatile fatty acids from the mixed liquor. The results obtained indicate that considerable stripping of hydrogen from the digester could be achieved at acceptable energy expenditure. However, the microbial removal of the hydrogen at these low concentrations is extremely slow and limits the applicability of this approach.